Ultra-high frequency connector



P 1967 B. o. WEINSCHEL 3,340,495

ULTRA-HIGH FREQUENCY CONNECTOR Filed Aug. 24, 1965 2 SheetsSheet l INVENTORS Bruno O. nschel Helmuf 800 r Edwin SEIsfe BY mm ATTORNEY ept. 5, 9 B. o. WEINSCHEL 3,340,495

ULTRA-HIGH FREQUENCY CONNECTOR Filed Aug. 24, 1965 2 Sheets-Sheet 2 FIG. 3

INVENTORS Bruno O Weinschel Helmur Bocher Edwin S.Els1'e ATTORNEY United States Patent ULTRA-HIGH FREQUENCY CONNECTOR Bruno 0. Wcinschel, Bethesda, Md., Helmut Bacher,

Arlington, Va., and Edwin S. Elste, Rockville, Md.,

assignors to Weinschel Engineering Co., Inc.,

Gaithersburg, Md., a corporation of Delaware Filed Aug. 24, 1965, Ser. No. 482,190 4 Claims. (Cl. 339-177) ABSTRACT OF THE DISCLOSURE A coaxial connector pair for frequencies up to 18 gc., compatible with standard connectors, in which the usual axial slots in the outer male connector are eliminated and a substantially flush fit is obtained with special centering means and precision tolerances. The inner female connector is also unslotted, with special biasing fingers to establish good radial connection with a reduceddiameter portion of the mating male connector.

This invention relates to a new improved coaxial connector pair comprising a male and a female connector, each element of which is compatible with the standard type N connector now commonly used.

Present-day requirements for military and space equipment are leading to the continually increasing use of higher and higher frequencies for coaxial microwave systems. Whereas formerly, the upper frequency for such equipment was in the order of 12 gc., there is now a requirement for equipment operating up to 18 gc., and at this upper limit, the standard type N connector which is used produces undesirable reflections and is incapable of giving satisfactory performance. However, to gain acceptance, any improved connector which is devised should be capable of mating with the present standard type N connector; in other words, it should be compatible. The present type N connector is reasonably satisfactory over the range up to 12 gc., but above this frequency, the following characteristics of the type N connector tend to produce undesirable reflections, leading to high VSWR values: first, in the present type N connector, the outer conductor of the male connector has four axial 'slots to permit resilient engagement; these slots are a major cause of undesirable reflections for the following reasons:

(a) Reflections are caused due to the change in characteristic impedance of this element considered as a part of a coaxial line.

(b) In order to make a positive contact with the female connector, the outer conductor with which the above element mates has a conical section to facilitate insertion of the element therein, and the slotted end of the male section is spread out somewhat in order to ensure resilient engagement when the two elements are fully mated. This, of course, involves compressing the ends of the male segments as they enter the conical section, until they come into engagement with an inner shoulder on the female element, the design being such that if the elements were perfectly dimensioned and positioned, a substantially flush interior surface would be obtained. However, in practice, this is very seldom the case, due to variations in both inner and outer diameter of the elements, as well as thickness of the end of the male ring and the female shoulder which it engages. This typically results in the creation of either an inside shoulder due to the edge of the male element protruding into the tubular passageway thus formed, or an outside shoulder due to the edge of the female element protruding because the actual diameters of the two elements do not coincide. This shoulder may be concentric, or if either of the elements is eccentric, it may exist only on part of the circumference, but in either case, the elfect is undesirable. Even a small shoulder of this type creates undesirable reflections, particularly at the high frequencies above 12 go. Another problem with the present slotted construction is the tendency, due to the rigidity and resilience of the prongs formed by the slots, for these prongs to bow in at the end as they are compressed, and to increase somewhat in internal diameter from the point of contact at the end of the prongs, and finally to return to its original diameter at the point where the prongs join the rest of the tubular structure. The resulting non-uniform configuration also is a source of reflections.

According to the present invention, the outer element of the male conductor is a cylindrical tubular element With no slots. This requires that the tolerances be held considerably closer than has been the practice, but on the other hand, the rigidity of the non-slotted constructions enables the use of closer tolerances since the entire unit is now much more rigid. By making typical tolerances plus or minus 0.0005 inch instead of plus or minus 0.0020 inch, as had been the previous practice, any shoulder formed at the area of junction is held to dimensions sufficiently small so that a good VSWR can be assured; however, even reducing the tolerances does not always guarantee against a certain amount of eccentricity, which must be avoided. It is therefore important to insure as close concentricity of the mating elements as possible. For example, good practice in present connectors permits a tolerance of 0.002 inch between extreme limits. To further improve concentricity, a spring-loaded ring may be used between the cylindrical male element and the tapered female element which receives it, the construction being such that the ring is spring-urged into the wedge area formed between the two elements so as to keep them concentric.

In the new connector, by virtue of holding the tolerances tighter, and with the addition of certain special features which will be described below, it is possible to do away with the slots and the resilient elements formed thereby, which have made it impossible to provide suflicient mechanical accuracy for the higher frequencies now required. It will be understood that this construction retains compatibility with the old type and connector, and if one of the new elements is mated with one of the old, while its operation at the highest frequency range may not be satisfactory, its overall operation up to 12 gc. will be at least equal to that of the standard type N connector, and in most cases will be improved, since one of the elements has been improved.

The next feature of improvement in the present connector is in the mating or contact between the inner conductors, the male pin and the inner female connector which receives it. Here again, in the present connector, the end of the male pin is stepped down or reduced in diameter in order to be received by a female connector having typically four slotted prongs similar to those described above, except much smaller in size. The prongs of the female connector are resiliently biased toward each other so that in the normal condition the edges of the four prongs touch each other when the connector is disengaged, these four ends being spread apart by the pin when the connector is engaged. This causes the slots to open up, and nominally to assume the original diameter of the inner bore, so that the prongs will be in good contact along their entire length with the reduced portion of the pin of the male element. However, in practice, the prongs do not bend back in exact straight lines when spread apart by the pin, but also tend to assume somewhat bowed or Patented Sept. 5, 1961 arcuate configuration, whereby contact is made with the pin at a point well spaced from the end of the flexible prongs, leaving a wedge-shaped gap between the end of the prong and the adjacent cylindrical surface of the pin. Since the very high frequency currents tend to follow the outside surface, this means that they go to the end of the prongs and then suffer a sharp reversal back for a certain distance until they come to the point of actual engagement of metallic contact between the pin and the inner surface of the prongs, and then reverse again and resume their original direction. This, of course, is a very bad condition for creating reflections and losses.

It will be noted that the very ends of the tines do not abut against the shoulder of the male pin, but leave a 'small axial gap. This is done deliberately, in order to avoid axial pressure between these elements due to the large forces which are developed when the coupling nut is screwed down. The construction is deliberately made such that the major mechanical force is taken by the much heavier outer conductors, since if it were transmitted through the inner conductors it would tend to cause buckling and displacement of the inner elements, which are typically attenuators or other precision elements which are both fragile in construction and which also require accurate physical placement for the desired precision of electrical values required. For this reason, the standard military specifications No. MIL-C-71B call for a gap of 0.026 inch between these elements. This is a relatively wide gap, which causes a large discontinuity, and to compensate for this, it has been the practice to design a ridge into the outer conductor of the male connector, which presumably offsets theeifect of this gap. However, at best this ridge would only compensate for the precise gap, and if the gap dimensions were not maintained, the effect of the ridge might even enhance the reflections rather than tending to suppress them. The allowable tolerance of plus or minus 0.02 inch readily permitted this undesired condition to appear in plugs which would otherwise pass the military specification. In order to minimize the effect of the above gap, the present invention again eliminates the slots of the female member, enabling closer tolerances to be employed, and also provides a construction, involving resilient elements, which suppresses or fills the radial gap above mentioned, and reduces the effect of the axial gap, while insuring contact between the outer surface of the male pin and the inner surface of the female element all the way up to the very end of the female element. Various attempts were made to provide these features, including the use of an inner ring between the male and female elements, the ring being axially spring loaded, so that it is again wedged into the space between the two. However, a better solution was finally devised in the use of spring-loaded torsion fingers of an inner sleeve within the female tubular element, the torsion fingers being so biased that they provide spring-loaded engagement between the supporting surfaces of the inner and outer mating elements, as will be explained in more detail below. Furthermore, these elements are constructed to ensure that contact will be made at the extreme end of the female member, which is the most important area, since it enables the current flowing on the surface of the inner conductor to take the Shortest possible path. Since the torsion elements, as will be explained below, are twisted so that the maximum angle occurs at the very end of the torsion elements, which end is made coextensive with the end of the tubular female member, the maximum engagement occurs at this point, and depending upon the closeness of the fit between the two elements, the torsional members are more or less flattened out into a generally circumferential arrangement, and the contact is increased as the closeness of the fit improves. However, in any case, the maximum contact is assured precisely at the point where it is most needed.

Another important feature of the present invention resides in the construction of the insulating bead which supports the central member within the grounded outer conductor. The bead made in accordance with the invention is much thinner in the axial dimension than has heretofore been employed, because it has been found, and verified both by mathematical theory and analysis and by actual test results, that there is a critical axial thickness of this bead, which must not be exceeded in order to allow operation up to 18 gc. The axial thickness should be less than one-half the wave length of the highest operating frequency (18 go.) at an interfering mode. The general reason for this is that the bead itself tends to act as a section of a transmission line supporting higher order modes of propagation, these being modes with circumferential variation of field, and by proper selection of dimensions and configurations, as will be shown below, these modes can be suppressed.

The, entire bead volume, at some wave lengths, tends to behave like a cavity resonating in some particular mode. The most troublesome circumferential mode is a TE mode with circumferential variations of the lowest order. Such a mode is analogous to the TR mode of a rectangular wave guide. It can be shown that the cut-off wave length of this type of wave is approximately equal to the average circumference of the coaxial transmission line structure, i.e., the cut-off wave length:

Where r and r are the inner and outer radii of the coaxial line.

The interference effect will only become bothersome when the length of the transmission line in which this load can exist is one-half of the Wave length of the load at the particular frequency. If the length of the head is one-half wave length, the bead region will act as an essentially resonant cavity coupled at both ends to the transmission line. This will change the impedance sufficiently to create excessive reflections.

A point concerning configuration of the head which is important isthat in the present construction an undercut is provided in the bead, providing essentially an annular groove therein; the purpose of this is to compensate for an effect due to the abrupt change in dielectric constant from air to polystyrene (when this is the insulating material used), which has a dielectric constant of about 2.56 over the frequency band from 0-18 gc. This produces a resultant distortion of the electric field so that unless the surface of the bead follows the concavity of the distortion so as to avoid the creation of normal field components which tend to cause reflections, the bead will serve as a potential source of reflections, which is typically the case with present construction. According to the invention, the bead configuration is therefore made such as to minimize this source of trouble. In this connection, it is very important that the dielectric constant of the material be maintained within proper limits, usually plus or minus 5 percent, since otherwise the entire purpose of the above design is frustrated. It is also very important to maintain the physical dimensions of the structure with respect to concentricity, perpendicularity, and dimensional tolerances.

In summary, it will be noted that in order to maintain a satisfactorily low VSWR, it is necessary that the individual causes of trouble he ferreted out, and that each of them be corrected in some manner, since each one of them can entirely invalidate the desired result if neglected. It is, therefore, necessary to provide a combination of features in order to provide a satisfactory connector for use at these extremely high frequencies, and these features cooperate with each other to the extent that each of them is required, since the absence of any one of them will frustrate the desired objective. Since each of the above elements mentioned is necessary to produce the final result, a satisfactory connector for use at 18 gc. must therefore employ a combination of all of the features.

The specific nature of our invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment, as shown in the accompanying drawings, in which:

FIG. 1 is an axial sectional view of the male and female members of a connector according to the invention, prior to connection;

FIG. 2 is an enlarged axial sectional view of the contact elements of the connector in mating engagement;

FIG. 3 is an enlarged view, partly in section, of the female center connector;

FIG. 4 is an end view of the female center connector;

FIG. 4A is a sectional view taken on line 4A4A of FIG. 2; and

FIG. 5 is an enlarged axial sectional view showing the insulating bead and the field configuration adjacent it.

Referring to FIG. 1, the two elements of the improved connector are shown. The coupling nut 2 of the male connector is of standard construction and dimensions, and has an internal thread 3 for mating with external thread 4 on the female connector, both of these elements being of standard construction and dimensions so that they can mate with standard type N connectors. Coupling nut 2 is rotatably mounted on outer shell 6 in the usual fashion, and shell 6 terminates at its forward end in a tubular mating member 7 which enters a tapered aperture 8 in the outer shell of the female connector, and as the outer nut 2 is screwed tight, the end of tubular element 7 finally is guided by the tapered portion into abutting contact with a shoulder 9 to form a smooth uninterrupted inner conducting surface for the transmission of the high frequency signals. In the usual type N connector the tubular shell 7 is provided with a number of axial slits, so that the end of the element is composed, in effect, of a circumferentially arranged series of arcuate prongs, which are radially deformed inwardly by the taper 8 in the final fully engaged position. This has the disadvantages enumerated in the preliminary discussion, and furthermore, in part because of the resilient construction, the tolerances required by military specifications for this equipment, which are the usual criterion, permit a radial deviation of up to .004 inch maximum. Thus a connector which passes specifications may still have an annular ring which, at the junction of the end of tubular element 7 and shoulder 9 (at 18 gc.) may be a serious source of reflections. In the present construction, this difliculty is obviated by making the tubular element 7 a continuous tubular element without the usual axial slits, and providing its external circumference with a thin sliding ring 11 which is spring urged in the forward direction by a spring 12. Making the tubular element rigid and unslotted enables the use of closer tolerences, thus assuring a better fit, and keeping any ridge or mismatch down to a sufficiently small value so that acceptable electrical performance can be obtained. In addition, the ring 11 is urged into engagement between the two mating elements, until it lies at that point of the tapered gap between them which its dimensions permit, as shown in FIG. 2, and serves both to improve the contact between the two, and more importantly, to ensure complete concentricity of the two elements. In this manner, the undesirable effects due to the standard construction are readily brought to the point of acceptable electrical performance, even at 18 gc. At the same time, either the male or female element can mate perfectly well with a standard type N connector with some improvement in performance, although the maximum improvement is not obtained unless both the elements are of improved construction.

The center conductor of the male connector 13, is supported within the outer shell by an insulator 14,-which diifers from the present type insulators used for this purpose in that it is considerably thinner, i.e., smaller in the axial dimension, and that it is also provided with two annular depressions or cum 17 and 17a on its two opposite faces as shown, so that the surface of the supporting insulation or bead on both sides thereof tends to follow the concavity of the distortion of the electric field as previously described, and as shown graphically in FIG. 5, in order to minimize another source of potential reflections not heretofore recognized.

Supported by bead 14 is the central conductor 13 which has a section 18 of somewhat larger diameter (such that the ratio of the inner diameter of tubular conductor 7 to the larger diameter leads to a characteristic impedance of 50 ohms) and a forward portion 19 of reduced diameter terminating in a sharp pin 21. This corresponds to the present construction of the center pin in the type N connector, except that again the tolerances are reduced from the present plus or minus .001 to plus or minus .0005 inch. This, of course, requires extra care and precision in both machining and assembling the elements, which is not done with the present type N connector because the results would not merit the extra difficulty involved, but which is worth the trouble in the present connector because of the better results obtained due to the construction also of the mating element on the female connector which will now be described.

The central mating element on the female connector 22, is mounted on a central bead 23,'similar in design and construction to central bead 14 of the male element. Its forwardor mating portion again comprises a continuous sleeve 24, which is not slotted as in the present standard type N connector, in order to overcome the disadvantages enumerated in the preliminary discussion. The inner diameter of the tubular shell 24 is made considerably larger than the outer diameter of pin 19,typically being .065 inch, while the inner diameter of tube 24 is 0.100 inch. Novel bridging elements are provided to fill in this gap, and these will now be described. Tubular shell 24 is actually a short cylindrical element which is soldered onto a shoulder 26 of the main body of the center female conductor 22 so as to make a very close fit. A further step in the central conductor is made at 27 leaving a very thin inner tubular projection 28, and this is axially slotted, for example, in six equidistant places as indicated at 29, leaving a number of thin resilient prongs 31 which are made coextensive in length with tubular element 24. Each of these prongs is then twisted so that it is distorted at its end as best shown in FIGS. 4 and 4A, so that the end 32 of these prongs form a series of resilient elements which extend from the inner circumference of tubular element 24 inwardly so that the other ends lie upon a circle which is smaller in diameter than the minimum outer diameter of the male pin portion 19. Thus when the male pin is engaged as shown in FIG. 4A, the torsional spring fingers 32 tend to be flattened out into a more nearly circular configuration, and are in positive spring contact with both the inner and the outer conductors. It will be noted that due to the torsional twist of each spring member, the maximum contact will be at the outer edge 28 of the spring fingers. The construction is such that a small gap 33 is provided between hte shoulder formed by the reduction of the diameter of the portion 19 of the pin, and the end of the tubular element 24. This is done deliberately so that no undue force can be exerted by the coupling on the relatively fragile central members of the connector. The tolerances are such that this gap varies between zero and .006 inch maximum, and this is unavoidable with this type of construction. However, because the ends of the conducting spring fingers 28 make good contact between the inner and outer conducting members 19 and 24 respectively, the undesirable effects of this gap are held to a minimum, since the current flow, which is partly shunted by the two conductors forming the gap acting as a capacitance element, and at the most the current must flow down the surface of the gap toward the center and then back again toward the outer surface of conductor 24, but at least it does not have to retrace its path as in the case where contact is not made at the extreme end of the tubular element 24. The undesirable effect of the gap is thus held to a minimum, and with the tolerances indicated, reflections due to this gap can be held to a satisfactory levelfor performance at 18 gc. It will be further noted that the action of the spring fingers 28 tends to center the central conductor 19 of the male pin, and thus avoid undesirable effects due to eccentricity. Furthermore, the twist of the spring fingers has been exaggerated in the drawings for the sake of clarity, and in practice, the spring fingers will be so spread out that they tend to lie in a nearly complete circle, except for the slots between them, and thus make contact over a substantial portion of the exterior surfaces of their respective conductors of which they engage.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of our invention as defined in the appended claims.

' We claim:

1. An ultra-high frequency coaxial connector for use at frequencies up to 18 gc. comprising a male connector unit and a female connector unit each having an outer conductive shell and an inner center conductor supported within the outer shell by an insulating bead,

(a) the outer shell of one of said units comprising a solid, unslotted tubular element protruding toward the other unit,

(b) the outer shell of said other unit having an outwardly tapering semi-conical aperture for receiving said tubular element, said aperture having an annular radial shoulder inwardly of its open end for receiving the end of said tubular element in abutting relationship, said shoulder and said end being very accurately dimensioned for a close fit,

(c) a thin sliding metal ring surrounding and in conductive contact with said tubular element, and means for biasing said ring forwardly so that it serves to center the tubular element within said tapering aperture when the two are mated,

, ((1) one of said center conductors having a cylindrical male element of a uniform main diameter, and having a cylindrical forward portion of reduced diameter, with an annular radial shoulder at the junction of the two diameters, said forward portion terminating in a tapered point,

(e) the other center conductor being a cylindrical conductor terminating in a tubular female member having the same uniform external diameter as the main diameter of the male element and having an internal diameter sufficiently larger than the reduced diameter portion of said male element to freely receive it with a radial gap between the two,

(f) a plurality of spring fingers circumferentially arranged within said radial gap, said fingers being located and biased so as to conductively extend across said radial gap at the open end of said tubular member when the male and female members are mated,

(g) each of said insulating beads being generally discshaped with the axis of the disc concentric with the axis of the connector, each face of the disc having a shallow annular groove in the region between the inner and outer conductors,

(h) the length of the tubular female member being such that when the outer shell portions of sections (a) and (b) are fully mated, there is a small axial gap between the end of said tubular female member and said annular radial shoulder of the male element, whereby no substantial axis pressure can be transmitted between the mated center conductors of I the connector.

ductor supported within the outer shell by an insulating bead,

(a) the outer shell of one of said units comprising a 8 solid, unslotted tubular element protruding toward the other unit, (b) the outer shell of said other unit having an outwardly tapering semi-conical aperture for receiving said tubular element, said aperture having an annular radial shoulder inwardly of its open end for receiv ing the end of said tubular element in abutting relationship, said shoulder and said end being very accurately dimensioned for a close fit, I

(c) one of said center conductors being a cylindrical male element of a uniform main diameter, and having a cylindrical forward portion of reduced diameter, with an annular radial shoulder at the junction of the two diameters, said forward portion terminating in a tapered point,

((1) the other center conductor being a cylindrical conductor terminating in a tubular female member having the same uniform external diameter as the main diameter of the male element and having an internal diameter sufficiently larger than the reduced diameter portion of said male element to freely receive it with a radial gap between the two,

(e) a plurality of spring fingers circumferentially arranged within said radial gap, said fingers being located and biased so as to conductively extend across said radial gap at the open end of said tubular member when the male and female members are mated,

(f) the length of the tubular female member being such that when the outer shell portions of sections (a) and (b) are fully mated, there is a small axial gap between the end of said tubular female member and said annular radial shoulder of the male element, whereby no substantial axial pressure can be transmitted between the mated center conductors of the connector.

3. An ultra-high frequency coaxial connector comprising a male connector unit and a female connector unit, each having an outer conductive shell and an inner center conductor supported within the outer shell by an insulated bead,

(a) one of said center conductors being a cylindrical male element of uniform main diameter having a cylindrical forward portion of reduced diameter, with an annular radial shoulder at the junction of the two diameters, said forward portion terminating in a tapered point, the other center conductor being a cylindrical conductor terminating in a tubular female member having the same uniform external diameter as the main diameter male element of section (a), and having an internal diameter sufiiciently larger than the reduced diameter portion of said male element to freely receive it with a radial gap between the two, F (b) a plurality of spring fingers circumferentially arranged within said radial gap, said fingers being located and biased so as to conductively extend across said radial gap at the open end of said tubular female member. 7 4. The invention according to claim 3, each of said spring fingers being a generally flat conductive spring element extending in a generally axial direction and fixed at its rear end to said other center conductor, and having a tortional twist therein at its free forward end.

References Cited UNITED STATES PATENTS p 3,245,027 4/1966 Ziegler 339-177 X 3,254,316 5/1966 McHenry 339l77 X FOREIGN PATENTS 1,092,535 11/1960 Germany.

MARVIN A. CHAMPION, Primary Examiner.

7a 1- v R- MOSE As istant Ex mi r 

3. AN ULTRA-HIGH FREQUENCY COAXIAL CONNECTOR COMPRISING A MALE CONNECTOR UNIT AND A FEMALE CONNECTOR UNIT, EACH HAVING AN OUTER CONDUCTIVE SHELL AND AN INNER CENTER CONDUCTOR SUPPORTED WITHIN THE OUTER SHELL BY AN INSULATED BEAD, (A) ONE OF SAID CENTER CONDUCTORS BEING A CYLINDRICAL MALE ELEMENT OF UNIFORM MAIN DIAMETER HAVING A CYLINDRICAL FORWARD PORTION OF REDUCED DIAMETER, WITH AN ANNULAR RADIAL SHOULDER AT THE JUNCTION OF THE TWO DIAMETERS, SAID FORWARD PORTION TERMINATING IN A TAPERED POINT, THE OTHER CENTER CONDUCTOR BEING A CYLINDRICAL CONDUCTOR TERMINATING IN A TUBULAR FEMALE MEMBER HAVING THE SAME UNIFORM EXTERNAL DIAMETER AS THE MAIN DIAMETER MALE ELEMENT OF SECTION (A), AND HAVING AN INTERNAL DIAMETER SUFFICIENTLY LARGER THAN THE REDUCED DIAMETER PORTION OF SAID MALE ELEMENT TO FREELY RECEIVE IT WITH A RADIAL GAP BETWEEN THE TWO, (B) A PLURALITY OF SPRING FINGERS CIRCUMFERENTIALLY ARRANGED WITHIN SAID RADIAL GAP, SAID FINGERS BEING LOCATED AND BIASED SO AS TO CONDUCTIVELY EXTEND ACROSS SAID RADIAL GAP AT THE OPEN END OF SAID TUBULAR FEMALE MEMBER. 